Some internal combustion engines include engine control systems that deactivate cylinders under low load situations. For example, an eight cylinder engine can be operated using four cylinders. When in deactivated mode, the engine is more fuel efficient due to reduced pumping losses. The engine control system deactivates cylinders under light load conditions. For example, light loads occur at steady state cruise when high engine power is not required, and in other situations such as idle and traveling downhill. The engine control system must be able to re-activate the cylinders quickly if the driver or driving conditions require more power than can be delivered in deactivated mode.
A flywheel starter generator (FSG) is connected to a crankshaft of the engine and increases available electrical power during vehicle operation. The FSG replaces a conventional starter, generator and flywheel. Various FSG arrangements are discussed in further detail in commonly owned U.S. Pat. No. 6,208,036 and in U.S. Pat. Nos. 6,202,776 and 6,040,634, which are all incorporated by reference.
The power output by the FSG can be used to reduce fuel consumption and emissions. In addition, the FSG can improve fuel economy by allowing the engine to shut off when the vehicle is temporarily stopped. When the vehicle accelerates from the temporary stop, the FSG restarts the engine.